Cast coated paper and method of making the same



Aug 1960 J. w. SMITH 2,950,214

CAST COATED PAPER AND METI-IOD OF MAKING THE SAME Filed March 25, 1957FINISHING ROLL COATING SYSTEM DIP ROLL COAGULANT BATH INVENTOR. JOl/A/W. S MITH ATTOQNE Y.

*- t i cc -'2 95a in n at P- r K r s -.:...a l sa Qua a E W v e gPatented Aug. 23, 3960 ing surface. Desirably, this surplus liquidcoating washes backwardly against an incoming paper web and allegedlyperforms the functions of flooding depressions in the sur- 2,950,214

face of the paper web which otherwise would become CAST CGATED PAPER ANDMETHOD OF air pockets during the casting operation, rejecting foamMAKING THE SAME and air bubbles in the coating, preventing foreign ma-John W. Smith, Chillicothe, oiiio, assigiior to The Mead terial f oniamng the poated p p surface, improving Corporation, Dayton, Ohio, acorporation of Ohio the distribution of coating on the paper Web,reducing difficulties with beads of coating forming on the casting Ffled19373561" 648327 surface beyond the edges of the paper web, and addi-Claims. (Cl. 117-64) tionally serves, together with the press rollpressure, to govern the final coat weight on the paper. However, afollowing patent, assigned to the assignee of the aforementioned surplusliquid-coating-material method, and 2;: igg ggi f g j ff ggg gg Eg ggi?15 relating to a method for continuously cleaningthe edges finiious in'hod of providing an irri proved mineral or Pi of a g drum i Indicatesthat cast-coating opera" tion nro ems are st' existent. meritedcast-coated pa er havin unusually high brwht- D ness and high gloss, ahigh degi ee of opacity and god :::-i? f i ?;:;d 2 35g? 11 532233 amniiyfor Priming inks And it incorporates the prim ii'ntadt with a caiiinsurface siill anothe i roce ss wa" ciple of coagulating certain coatinadhesives to obtain g D n Pd a k Vino im raved fical Dre artias notadvanced which allegedly eliminated the liability of en- 52122 3 5 g l atrapping air between a drum and a coated paper surface An early pro osalfor producin zi lossy rrinera applied thereio' This process Involvesapplying a fimd coated a er embodied the a licafiion 0f an a ueou scoatmg to a r-novmg paper- Pressing :[he freshly 0 t PP v b t 1' coatedsurface into contact With a chrome casting surface, 31 222 32523 323 ggz ig gg g 2 and maintaining a circulating pool of water in the castingished chromium driin'i surfa e drying the coatin w l ii e mp thereby TheWfate-r paol rewets i sun it remained in such contact and then s ri pinthe coated cO-ated Surface dlsplaces an m snauowpocfiets which paperfrom mp drum surface This .131 P0531 was fi might become non-glossyareas on the finished sheet, and referred to as a cal ndering ratherthan a coating op raby commuously Washmg the edges of the castmg tionand the mineral coated pa er allegedly produced Pam-y overcom-es theprom??? of edge-beads' i? thereby w s characterized as cast surfacepaper The if i progss 1S f i 5? sufficlentlg loixgpressme in t e castingmp so at t ere is no re istri ution of term mineral-coated a er relaedto a a r corn risg a filbmus base i f on on: both g a 35 the coatingitself, independently of the water pool, the tinuous la er of mineral ori ine nt com osition which required Intimacy OI csmtact bitween thesurface of the covers theyfibars of fhe has; g fins the hgnnws batwmlncoating and the chromium casting surface cannot be ohthe fibers on thesurface of the base 50 that when the pperaqon pr-eSsures high. eiloughtogive coated paper is pressed against a heatd chromium drum distributingaction, disperse a portion or the coating in surface wh le the coatinisin a lii hl plastic condition 40 the water and certau} of theSuspended olids pressthe coatin is rend red zcmnar tiv lyy on plast ch9g0: ent in the coating composition are inherently transferred \4 L- L4L1 VJ. 1v I it is remo i/ed rom this surfac The min ral coatin to theWater pool Whlch thereby becomes milky m api c. c g composition wasapplied to the paper in the form of an ggi gf pfggi g gaggi cl gig zoghiirefidriei iglelalsio aqueous suspension of pigment (usually clay,satin white, d h y 1 a y etc.) and an adhesive or binding a ent (usuallycasein or E to t 6 paper 15 lost dram and such Starch) loss is anobvious economic liability.

As previously pointed out pi ment binders for c t- The use of starch 0cas e b- W for cast-coated paper leavsi iii uzh io b d cfisii d Inge;mate? p i at gauge the coatmg Surface to suck and not comp etey re easefrom the finishing surface thereby example, casein which is preferred tostarch in prepar- 50 effecting surface defects in the ultimatecast-coated paper ing cast-coated paper, has the characteristics of slowproduct or preventin operations entirely. As a proposed water releaseand low drying rates resistance to ink a remedy, it has been suggestedthat release a ents such as penetration, deleterious effects onbrightness and opacity a film of olea inous material be applied to achrom um or the finished paper when present in the required quancastingdrum before and/or durm the time that the tities, and if heated toogreatly durin drying may show D P. 1: a loss of binding ability beforeor du ring drum finishing g g g i i ggg fii s casunhg lunmon operations.Moreover, there are other disadvantages and g a on a c mmmm Pastmg mglaring defects such as having thfi coatino surfaca Stick nowever, isnecessarily dependent on continuously main- 1: a o a v to the drumfinishing surface after drying thereon, having :32? 3 g g on i drum andthis 18 (16.- air bubbles and occasional particles of foreign matter infi i: y a S e (-meramr W 0 must (.zarefuuy Watcn the coating to formdull spots the formation of holes e mshefi paper as It leaves thechrommm drum and cracks, and other defects in the cast surface of the paer j or zi the amount of llqu-1d Oleagimius and the formation of edgebeads of coating on portions on t e c onimm drum and/or 111 the coatmgof the drying drum which extend beyond the ed es of co or g g i adequaterelease of the dated a the paper web, all of which result from attemptsto carry gi g? i 3 ,2 1? ig gg i fi g desir d C St out theaforementioned s a minerabcoated Daper Propg al for Producmg a glossycoated paperhas Proven entirely satisfactory. Now in Subsequentpioposals have been directed to methods g fpresent Invention there hasbeen I covere a me 0 or continuousl roducin mn r l for partiallyovercoming certain of thes dlsadvantar-es y P e 1 s cast-coated paperhaving outstanding characteristics, and defectsexample, 0116 P hasSuggested which method is not subject to the disadvantages of thepooling surplus liquid coating materia at the nip Where the paper web ispressed into contact with a castprior art processes.

Generally, the present invention comprises applying 3 an aqueous,pigmented coating composition containing a pigment binder to' a paperweb and thereafter passing the web carrying the coating through acoagulant bath. As a result, the binding or adhesive component of thefreshly applied coating without'substantial drying, .is converted by thecoagulant into a gel, but in acordance with the invention, the coagulantis applied in such a way as to prevent distortion of the coating film.After substantially complete gelation of the pigment binder, the coatingis then passed over a press roll and transferred to a casting surface,as for example, a methyl silicone resin casting surface chemicallybonded to a metal substrate. While a Small amount of the coagulant solu-7 tion may accumulate as a pool in the nip between the It is accordinglyan object of'the invention to provide I a cast-surfaced. coated paperhaving improved optical properties.

Another object is to provide a cast-surfaced coated paper havingunusually high brightness and opacity and high gloss.

Another object is to provide a cast-surfaced coated paper having anenhanced aflinity for printing inks.

Still another object is to provide an improved method for continuouslyproducing such a paper having said characteristics, which methodfacilitates ready release of the coating from the casting surface anddecreases normal surface defects on the paper. 7

Another object is to provide a method of the foregoing type adapted torelatively high speed production.

' Another object is to avoid operating defects, such as the occurrenceof edge beads, associated with prior processes referred to hereinbefore.

Another object is to provide a method which is adapted to Widecommercial utilization and which produces a,

cast-surfaced paper product that can be used widely.

Numerous other objects of this invention will more fully hereinafterappear.

The accompanying drawing portrays diagrammatically one arrangement ofequipment which has been satisfactorily employed for practicing thepresent invention.

Referring to the drawing, the paper web to be coated is drawn from aroll 10 of suitable paper base stock, and

the web 11, is led over guide rolls 12 and 13 to pass through theapparatus in the coating color applying zone. ,7

In this modification, the web passes through the nip of the coatingapplication rolls 14, 15 where a predetermined amount of coatingsuspension is applied thereto and distributed with sufiicient uniformityover the web surface to give the desired weight of coating material perunit area on the web.

The present invention permits the use of commonly used aqueous,pigmented coatings, containing only such pigments, adhesives andadditives as are normally used in preparing, pigmented coatings forprinting.

In other I Words, a normally adhesive'coating material such as asuspension or colloidal solution of pigment and adhesive material inasuspending or solvent fluid is applied by such apparatus to the paperweb but application thereof is desirably made in such a manner as toprovide the coated .of the adhesive coating material appear to remainundisturbed after the coagulant reaction, the coating nevertheless hasits characteristics temporarily modified sothat the adhesive tendencywhich would normally be eifective between thecoating material and acasting surface is so greatly reduced, that the surface coating materialdoes not adhere to the casting surface after drying, but neverthelessacquires the smoothed surface characteristics of the casting surface.In. addition, there is no substantial or practically appreciabledisturbance of the smoothed surface coating as it separates completelyfrom the casting surface as a high gloss coated paper.

In practical operations, utilizing the invention and the apparatusillustrated, under commercialoperating conditions, this modification ofthe coating prior to a finishing operation on a casting surface, iseffected by coagulating the mineral surface coating, after the coatinghas been applied evenly to the paper web, but before the coating isbrought into contact with the casting surface. In actual practice,satisfactory results have been obtained by the modifying and/orstabilizing action of this invention by wrapping the freshly coatedpaper, Without substantial drying, coated side out, tightly around roll16 which dips into the coagulant solution or bath contained in a tub 17.As illustrated, the coated paper is rolled into and out of thecoagulating bath in such a way that the coagulant only contacts thecoated surface of the paper web and is reactive with the coating fromthe time the coating material is first brought into contact with thecoagulant, until substantially complete gelation of the coating adhesivehas been effected. In this manner, distortion of the coating film isprevented and following gelation, the coated paper 11 is transferred bypress roll 18, through nip 19 to a finishing roll 20 having a smoothlybufied methyl silicone casting surface, such as disclosed in co-pendingapplication, Serial No. 635,974, filed I anuary 24, 1957. Roll 20, whichis heated, has its smooth silicone surface in contact with thestabilized but moldable coating until the coating spontaneously releasesfrom the silicone surface after it is substantially completely dried andis thereafter removed by tension roll 21. The dried coated paper isthereafter rolled up on winder roll 22.

The accompanying drawing illustrates one form of apparatus for applyingthe desired quantity of coating smoothly to the web. To accomplish'thisresult, the

color solids should preferably be adjusted so that the coating is nottoo viscous for easy application, nor so dilute as to be incapable offorming a tough gel. Relatively high solids content coating suspensions,e.g. of the order of 45%65% solids or more, have been used successfullyand, as a general rule, the preferred percentage of solids in thecoating is governed by the type and quantity of adhesive selectedfor-the color. For example, higher adhesive contents require lowersolids, and latex may be used at higher solids than protein adhesives.In the apparatus shown, the coating color is fed through a suitablesupply line and by suitable means to one or more discharge pipes ornozzles, indicated diagrammatically at 23, and into the nip betweenrolls 15 and 24- which have the direction of rotation as indicated, thecolor forming a pool 25. Doctor 26, as shown, functions to maintain thepool in the aforesaid nip between rolls 15 and 24 and any suitable wellknown doctoring means may be employed. Color from pool 25 preferably isallowed to overflow at both ends of the nip, and is recirculated. Suchoverflow of the pool provides a means for removal of grit whichotherwise would accumulate in the pool.

Roll 24 runs in contact with the application roll 15 and provides formetering thereon a regulated quantity of uniformly distributed coatingmaterial which in turn is transferred from roll 15 to the traveling webof paper as it passes through the nip of the application rolls 14, 15.

The coating apparatus shown is a reverse roll system and has been foundto be very satisfactory and effective for transferring from the troughof coating material or so-called coating color, between rolls 15 and 24,accurately controlled amounts of the coating material. With high solidscontent coating colors of the order of as high 6 plastorneter reading ofthe order of 80 to 140 P. & I. when measured with a /s inch ball. And ifone or more of these three rolls is hard surfaced, i.e., of metal,Stonite, or the like, then its adjacent roll is preferably resilientsurfaced. For example, the following combinations of these coatingmechanism rolls have been found commercially suitable and are presentedin illustration but not in limitation of the invention.

Roll No.

Type of Roll By Combination l40P&J- 136P&J 8OP&.T 140P&J. Meta -112P&Il30P&J Stonite. 112P&J--- Metal 1l2P&.T 1121 8123.

fluent and flowable so that it may be thus accurately controlled as toquantity and general distribution. The coating material passing incontrolled amount through the nip of the rolls 15, 24 is carried on thesurface of roll as it travels up toward the paper web, to transfer thedesired quantity of coating material for the predetermined coat weightdesired, and in such condition of fiowability that the color will begenerally distributed across the surface of the roll 15 as it movestoward the paper and application nip of rolls in such condition offlowability and such distribution when brought in contact with the paperweb by roll 15 turning in a direction opposite to the direction oftravel of the paper web, there will be transferred to the web asubstantially uniformly distributed layer or film of coating materialwhich is of considerable and unexpected smoothness. The coatingmaterials commonly used, contain a substantial amount of adhesivematerial such as casein. However, by the disclosed reverse roll system,there is sufficient working of the coating color both before it passesinto the application nip of the rolls 14, 15, and also within the nip byreason of the reverse turning of roll 50, so that even high solidscontent coating colors will be made sufficiently fluid, for securing thedesired accurate coat weight, and the uniform distribution -of the filmupon the surface of the paper web. Moreover, the apparatus referred to,when using somewhat lower solids content colors with greatly reducedviscosity and corresponding increased fiowability, has been verysatisfactory in applying the desired quantity and uniform disleaving asurface which is sufficiently smooth so that it' may be subsequentlycoagulated and dried on a. finishing surface to give the desired highgloss coated paper. In the latter case, rolls 15, 24- are preferablyoperated at a low pressure of the order of 10 pounds per lineal inch, orlower and may even be operated at a gap amounting to as much as .005inch.

Again, referring to the coating apparatus illustrated, very satisfactoryresults have been attained when rolls 14 and 15 were rubber coveredrolls; roll 14 having a plastorneter reading of about 136 P. & 3. androll 15 having a plastorneter reading of about 112 P. 5: 3. Rolls 1 and15 may be operated with a pressure therebetween varying duringoperation, for example from about 1 to 25 pounds per lineal inch, withsatisfactory results having been obtained at a pressure of preferablyaoout 10 pounds per lineal inch. Roll 24 in this connection was a hardsurfaced Stenite roli. Rolls 18 and 21 had plastometer readings of and32 8: 5. respectively, while roll 29 was a metal roll, having a smoothlybuffed methyl silicone casting surface, such as disclosed in copendingapplication, supra. Roll 16 was a corrosion resistant roll such asstainless steel. More generally, however, it has been found that rolls14, 15 and 24 may all be resilient surface type rolls, such as rubbercovered rolls having a All plastometer values were measured with a /sinch P. & J. ball.

The pressure in operation between rolls 18 and 20 may be varied over asubstantial range; for example, from about 50 to 150 pounds per linealinch, with satisfactory results having been obtained at a pressure ofabout 75 pounds per lineal inch. In thisconnection, it has been foundthat the upper pressure limit is determined by the strength or toughnessof the gelled coating. And the pressure between rolls 18 and 20 may bevaried over wide limits so long as sufficient pressure is used to insureintimate contact between the coating surface and the casting surface.

Various coating materials may be employed in practicing thepresent'invention and as indicated by the formulations hereinafter setforth, the coating material generally comprises a mineral and anadhesive in aqueous medium. Both the adhesive content and the totalsolids content of the coating materials to be used are predicated on theultimate high gloss coated paper desired and for highly satisfactoryoperations, such adhesive and total solids contents may be somewhatcritical. For example, it has been found that the preferred range ofadhesive contents is of the order of 12%-20%, although more or lessadhesive can be used if special end-use requirements of the ultimatehigh gloss paper product so dictate. Moreover, if starch is used inadmixture in the adhesive, more total adhesive is required than if it isnot so used. Generally, the higher region of the adhesive content rangeis useful in preparing papers for offset printing, while the lower rangehas been found useful for letterpress printing.

A color formula which has been found to function satisfactorily in thepracticing of the invention is of the following composition, wherein theparts by weight are taken on a dry basis:

Example I Parts by weight Clay (English coating clay) 42.0 Calciumcarbonate 42.0

Casein (Argentina) 12.0

Caustic soda (parts per parts of casein) 6.0 Sodium pyrophosphate 0.75Calcium stearate 0.5 Dow 512-R latex (butadiene-styrene copolymer Diisobutylphenoxyethoxyethyldimethylbenzylanr moniumchloride, monohydrate(Hyamine 1622, Rohm & Haas C0.) 0.05

' Example 11 a Parts by weight Clay (English coating clay) 42.0 Calciumcarbonate 42.0 Soya protein (refined) 12.0 Ammonia, 26 B. (parts per 100parts of protein) 12.0 Dow 512R latex 4.0 Sodium pyrophosphate 0.75Calcium stearate 0.5 Hyamine 1622 0.05

Example III Clay (English coating clay) 38.0 Calcium carbonate 41.0Satin white Alpha protein 12.0

Ammonia, 26 B. (parts per 100 parts of protein) 12.0 Dow 512-R latex 4.0

Sodium pyrophosphate 0.75

Calcium stearate 0.5 Hyamine 1622 0.05

Example VI Clay (domestic coating clay) 81.0 Soya protein (refined) 12.0

Azite (dicyandiamide) (parts per 100 parts of protein) 25.0 Ammonia, 26B. (parts per 100 parts of protein)- 15.0 Sodium pyrophosphate 0.75Sulphonatedtallow (Vegetol) 1.0 Calcium stearate 0.5

Dow 512-R latex 7.0 Hyamine 1622 0.1

Particularly satisfactory high gloss coated papers of the invention wereproduced by applying the coating of Example I, supra, to the web 11 asshown in the drawing. While the layer of coating was still suflicientlymobile or deformable, the web, coated side out, was tightly wrappedaround roll 16, as shown, thereby rolling the coated paper into and outof the coagulatingibath and concomitantly initiating gelling of theadhesive componentof the coating. Roll 16 is so spaced from nip 19 as topermit substantially complete gelation during the time the coating onthe web is treatedwith coagulant until the web is transferred by pressroll 18 tothe heated silicone resin finishing roll 20. In this instance,the coating, after coagulating but prior to casting, was in the form ofa nontacky, tough but deformable gel. And the resulting cast coatedpaper had a Bausch & Lomb gloss of 86.0 and was without megascopicsurface defects, such as are frequently found in cast-surfaced coatedpapers; This paper also had enhanced affinity for printing inks as.compared to cast-surfaced coated paper not produced in accordance withthis invention.

Even when using less expensive pigments such as domestic' coating clayin color formulae when practicing this invention,.it has been found thatcast-surfaced coated papers have unexpectedly high brightness andopacity. In this connection, reference is made to the following chartwhich depicts typical brightness and opacity improvement of cast surfacecoated papers as attained by this inventron, using the coagulatingagents designated and the coatmg formula of Example VI, supra:

G.E. Brightness Banach & Lornb TAPPI Coagulating Agent Opacity Usedallsolutions 10% by weight solid material Ooagulated Not Goag-ulated Not 7Coagulated Coagulated Aluminum Sulfate"- 80. 0 78.0 97. 0 96.0 ZincSulfate 80. 2 78.3 97. 5 96. 2 Magnesium Chloride. 79. 7 78. 8 97. 0 96.3 Calcium Chloride.... 79. 7 78. 8 97. 7 96. 3 Zine Chloride 80.0 79.097. 3 96.1 Barium Ghl0ride. 80.5 77. 7 97.0 96. 8 Lead Acetate 80.1 77.697. 0 96.2 Zinc Acetate 81. 8 78.2 97. 3 96. 2

G.E. Brightness Bausch & Lomb TAPPI Opacity Weight Percent Zinc AcetateOoagulated Not Coagulated Not Coagulated Ooagulated The toughness of thegel preferably is adjusted so that the coatingis plastic enough todeform under the pressure applied at casting nip 19 yet tough enough sothat absolutely none of the coating is removed in this nip. It has beenfound that proper gel toughness may be obtained *by proper selection ofan electrolyte within the group of preferred coagulants, by varying thecoagulating bath temperature and concentration, and by altering the time.of exposure of the coating to the reaction of the coagulant prior tocasting. Selection of the coagulant depends upon the particular adhesiveemployed in the coating, but it should be a colorless, water-solubleelectrolyte, which is neither a strong acid nor a strong alkali. Asnoted hereinbefore, these factors can be varied over wide limits withoutcritically affecting the operation of the process. When starch is usedalone, it is difiicult to obtain a sufliciently tough gel to withstandthe casting operation. When casein, soya protein, synthetic rubber latexand similar materials or their mixtures are used as the adhesive, orwhen mixed with less than an equal amount of starch, the soluble saltsof polyvalent metals and weak organic acids perform best. The acetates,or formates of calcium, zinc, barium, lead and aluminum are preferredcoagulants, because they function adequately to give the desiredeffects, yet do not reduce the pH of the finished paper too greatly.Sulfates, chlorides, and other strong 'acid salts of these metals may beused where an acid pH is not objectionable in the paper or when a highlyalkaline mineral such as satin white is used in the coating color Q! inan amount sufiicient to neutralize the residual acidity of thecoagulant.

In general, it has been found that water soluble compounds within thegroup of calcium, zinc, barium, lead, magnesium, cadmium or aluminumsalts of formic, acetic, citric, tartaric, lactic, hydrochloric andsulfuric acids provide suitable coagulants for this invention. Moreover,under certain conditions free organic acids such as lactic acid may beeffective coagulants. And the concentration of the coagulant may, ofcourse, be varied to compensate for its specific activity, thetemperature of the coagulant bath and the speed of operation.

Generally, the more active coagulants produce the greatest opticalimprovement in the finished paper. Coagulant concentrations of from 1 to20 percent by weight in water are useful, the preferred range being from3 to 7 percent. And, gelling activity increases with the concentrationof the coagulant and in addition, such activity also increases with thecoagulant bath temperature. bath temperature from 1 to 90 C. may beemployed so long as the coating, after coagulating and just prior tocasting, is in the form of a non-tacky, tough but deformable gel. And toattain such a gel condition, the time of exposure of the coating to thecoagulant is preferably of the order of 0.5 to 5.0 seconds, or more,i.e., the time interval for transferring the treated coating fromcoagulant bath 17 to the nip 19.

The surface temperature of the casting drum 29 is preferably from 80 C.to 100 C. during the drying cycle for producing the cast-surfaced coatedpaper having unusually high brightness and opacity and high gloss ofthis invention, although temperatures ranging from 65 C. to as high as105 C. have been used without harmful results. It has been found thattemperatures approaching 90-100 C. are advantageous when the more activecoagulants are employed.

Ordinarily, after the paper web 11, the coating of which has been gelledby coagulation, has been maintained in contact with the drum 20 untildry, the paper is readily stripped off the drum 20 by roll 21. As pre-'viously set forth, drum 2% preferably has a silicone resin surface but,during some operations in accordance with this invention, it was foundthat an ordinary metal drum such as a chromium surfaced drum could beutilized and that satisfactory release of the coating was obtained.Presumably, the coating in its gelled condition becomes so stabilized attimes that it separates completely from the smoothing, clean surfacedrum member and is readily separated therefrom by roll 21.

However, it has been found that any required As previously pointed out,a small amount of the coagulant solution may accumulate as a pool in thenip 19 between the press roll 18 and the casting surface 20. While ithas been found that such a pool merely consists of clear, excesscoagulant that is squeezed from the surface of the coating at thecasting nip, it may, nevertheless, be desired in some operations toprovide a rotating brush or a felt covered roll 27 between the nip 19and tension roll 21 for maintaining a clean casting surface,substantially free of coagulant solution. In addition, it is preferablethat the coagulant in the bath =17 be recirculated by any well knownmeans during operations to maintain uniformity of the coagulant in thebath.

While the methods, apparatus and products herein described are for thepurpose of illustration only, it is to be understood that the presentinvention includes all modifications and equivalents which fall withinthe scope of the invention which is defined by the appended claims.

What is claimed is:

1. In the coating of paper to provide a cast-surfaced mineral coatedpaper having unusually high brightness and opacity and high gloss withenhanced aflinity for receiving printing and the like, the process whichcomprises the steps of applying and distributing a predetermined i0 7and metered quantity of fluent mineral coating consisting essentially ofan aqueous suspension of pigment and adhesive material to form asubstantially smooth surface coating on the paper, bringing the coatedsurface of said paper into contact with an adhesive coagulatingelectrolyte while said coating is still fluent on said paper toprogressively convert said adhseive into a substantially toughdeformable gel while maintaining a substantially uniform and smoothsurfaced layer of coating, bringing said coated surface of said paperinto contact with a. substantially smooth casting surface after saidadhesive has been converted to said tough deformable gel, and dryingsaid coating while said coating is in contact with said substantiallysmooth casting surface, and removing said coated paper from said castingsurface.

2. In the manufacture of cast-surfaced mineral coated paper havingimproved optical properties and enhanced aflinity for printing inks, thesteps comprising progressively coagulating the coating while stillmobile and fluent and deformable on the paper by direct contact with acoagulating electrolyte to stabilize the coating against adhesion to thesurface of a casting surface, thereafter bringing said coating while sostabilized in intimate contact with said casting surface and drying saidcoating on said casting surface, separating said coating from saidcasting surface.

3. The process of making cast-surfaced mineral coated paper havingunusually high brightness and opacity and high gloss which comprisesapplying to a web of paper a coating color consisting essentially of anaqueous suspension of pigment and adhesive material, said coating colorhaving from about 45% to about 65 total solids and having said adhesivepresent in an amount between about 12% and about 20% of said solids,progressively coagulating said coating to form a substantially nontackytough deformable gel by contacting said coating color with a watersolution of an adhesive coagulating electrolyte, and thereafter bringingsaid coating in contact with a casting surface.

4. In the coating of paper to provide a cast-surfaced mineral coatedpaper having unusually high brightness and opacity and high gloss withenhanced afiinity for receiving printing and the like, the process whichcomprises the steps of applying an aqueous suspension of pigment andadhesive material of approximately 45 to 65% solids content to the paperin an initially fluent and deformable condition to form a coatingthereon, stabilizing said coating against adhesion to the surface of aheated casting surface by progressively coagulating said coating with acoagulating electrolyte sufliciently to form a non-tacky'toughdeformable gel, thereafter bringing said coating in intimate contactwith said casting surface, drying said coating against said castingsurface, and withdrawing said paper from said casting surface withseparation of the coating therefrom.

5. The process of producing cast-surfaced mineral coated paper of thecharacter described comprising applying to the surface of a web of papera coating color consisting essentially of an aqueous suspension ofpigment and adhesive material, said coating color having from about 45%to about 65% total solids and having said adhesive present in an amountbetween about 12% and about 20% based on the weight of said totalsolids, said adhesive being selected from the group consisting of caseinand soya protein and mixtures thereof with latex, and after applicationof said coating color progressively coagulating said adhesive to a toughdeformable gel by contacting said coating color with a water solution ofa coagulating agent selected from the group consisting of solublecalcium, zinc, barium, lead and aluminum salts of formic, acetic,citric, tartaric, lactic, hydrochloric and sulfuric acids, squeezing offthe excess solution, thereafter bringing said coating in intimatecontact with a heated smoothly finished casting surface, drying saidcoating against said casting surface, and withdrawing said paper 1 1from said casting surface with substantially complete separation of thecoating therefrom.

6. Process as defined in claim 5, in which the. coagulation agent iscalcium formate.

7. Process as defined in claim 5, in which the coagulation agent isaluminum sulfate.

8. Process as defined in claim 5, in which the coagulation agent iscalcium lactate.

9. Cast surfaced coated paper produced in accordance with the process ofclaim 5.

10. The process of producing cast-surfaced mineral coated paper of thecharacter described comprising applying to the .surface of a Web ofpaper a coating color con sisting essentially of an aqueous suspensionof pigment and adhesivetmaterial, said coating color having from about45% to about 65% total solids and having said adhesive present in anamount between about 12% and about 20% based on the weight of said totalsolids, and after application of said coating color progressivelycoagulating said adhesiveto a tough deformable gel by contacting saidcoating color with a water solution of a coagulating agent selected fromthe group consisting of soluble polyvalent metal salts of formic,acetic, citric, tartaric, lactic, hydrochloric and sulfuric acids,squeezing ofi the excess solution, thereafter bringing said coating inintimate contact with a heated smoothly finished casting surface, dryingsaid coating against said casting surface, and thereafter withdrawingsaid paper from said casting surface with substantially completeseparation of the coating therefrom.

11. Process as defined in claim 10, in which the coagulation agent iscadmium sulfate.

12. Process as defined in claim 10, in which the coagulation agent iszinc acetate.

13. Process as defined in claim 10, in which the coagu lating agent is amixture of calcium formate and zinc acetate.

14. In the cast-surfaced coating of paper of the character described toproduce surface characteristics adapted for receiving printing and thelike, the method of forming a smooth surface on a layerof coatingcomposition applied to paper which comprises the steps of stabilizingsaid coating prior to drying thereof against adhesion to the surface ofa heated casting surface by progressively coagulating said coating witha coagulating electrolyte sufficiently to form a non-tacky toughdeformable: gel, thereafter bringing said coating in intimate contactWith said casting surface, drying said coating against said castingsurface, and withdrawing said paper from said casting surface withsubstantially complete separation of the coating therefrom.

15. The process of making cast-surfaced mineral coated 1 paper havingunusually high brightness and opacity and high gloss which comprisesapplying to a web of'paper a fluent mineral coating color consistingessentially of an aqueous suspension of pigment and adhesive material,said coating color having from about 45% to about 65% total solids andhaving said adhesive present in anamount between about 12% and about 20%of said solids, said adhesive selected from the group consisting ofcasein and soya protein and mixtures thereof with latex, progressivelycoagulating said coating to form a substantially nontacky toughdeformable gel by contacting said coating color with a water solution ofan adhesive coagulating electrolyte, and thereafter bringing and dryingsaid coating in intimate contact with a casting surface.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN THE COATING OF PAPER TO PROVIDE A COAST-SURFACED MINERAL COATEDPAPER HAVING UNUSUALLY HIGH BRIGHTNESS AND OPACITY AND HAVING GLOSS WITHENHANCED AFFINITY FOR RECEIVING PRINTING AND LIKE, THE PROCESS WHICHCOMPRISES THE STEPS OF APPLYING AND DISTRIBUTING A PREDETERMINED ANDMETERED QUANTITY OF FLUENT MINERAL COATING CONSISTING ESSENTIALLY OF ANAQUEOUS SUSPENSION OF PIGMENT AND ADHESSIVE MATERIAL TO FORM ASUBATANTIALLY SMOOTH SURFACE COATING ON THE PAPER, BRINGING THE COATEDSURFACE OF SAID PAPER INTO CONTACT WITH AN ADHESIVE COAGULATINGELECTROLYTE WHILE SAID COATING IS STILL FLUENT ON SAID PAPER TOPROGRESSIVELY CONVERT SAID ADHSEIVE INTO A SUBSTANTIALLY TOUGHDEFORMABLE GEL WHILE MAINTAINING A SUBSTANTIALLY UNIFORM AND SMOOTHSURFACE LAYER OF COATING, BRINGING SAID COATED SURFACE OF SAID PAPERINTO CONTACT WITH A SUBSTANTIALLY SMOOTH CASTING SURFACE AFTER SAIDADHESIVE HAS BEEN CONVERTED TO SAID TOUGH DEFORMABLE GEL, AND DRYINGCOATING WHILE SAID COATING IS IN CONTACT WITH SAID SUBSTANTIALLY SMOOTHCASTING SURFACE, AND REMOVING SAID COATED PAPER FROM SAID CASTINGSURFACE.